1. Field of the Invention
The present invention relates to noise power estimation apparatuses and methods, and more particularly, to a noise power estimation apparatus and method for estimating noise power and noise interference used for signal quality measurement in radio receivers in various radio communication systems such as orthogonal frequency division multiplexing access (OFDMA) communication systems.
2. Description of the Related Art
With the rapid progress of recent communication system technologies, it becomes necessary to estimate noise power in communication to calculate a channel quality indicator (CQI) since adaptive modulation or the like is used as a modulation technology. In addition, since an accurate CQI leads to an improvement in system performance, it is important that noise power be calculated accurately.
In a conventional code division multiple access (CDMA) system, for example, a base station adds a power control signal to a forward link (from the base station to a mobile terminal) signal and sends them to the mobile terminal to control the power of the mobile terminal in order to control the power of the reverse link (from the mobile terminal to the base station) To determine the power control signal, information about a signal to interference power ratio (SIR, a desired signal to interference ratio in power) estimated at the upstream receiver side is used. In general, the power level used for transmission from the mobile terminal to the base station corresponds to the lowest minimum receiving quality at the base station. This is for system stability and capacity improvement. If an excessive power level is used, it may cause extra interference or excessive traffic in the entire system, reducing the efficiency of the system.
In the conventional CDMA system, because the interference power I is sufficiently higher than the signal power S, the variance of a receiving signal is obtained to easily calculate the noise power (for example, see PCT International Patent Application Publication in Japanese NO. 2004-533783).
In a conventional OFDMA system, because the signal power S is higher than the interference power I, the method used in CDMA cannot be used. Consequently, a replica signal is generated from a received pilot signal and the noise power is estimated from the distance (shift) between the replica signal and the actually received signal point (see Japanese Unexamined Patent Application Publication No. 2005-328311).